The present invention relates generally to a calibration method for calibrating dimensional measuring probes. More particularly, the calibration method eliminates errors that are caused by inadvertent movement of the gauges.
Ultrasonic dimensional measuring probes are frequently used to measure the thickness of a target, or a precise distance between components. These range finders have been applied to such diverse areas as gauging thickness of cold rolled steel, positioning parts for robotic assembly, sorting parts by thickness, determining the liquid levels in containers, and picking out cross threaded caps on bottles. At times, the measurements must be accurate to within .+-.0.002 inch for thickness and .+-.0.001 inch for distance. However, movement of the sensor relative to the target surface and/or movement of a pair of opposing sensors relative to one another can introduce errors in the measured target thickness. The problem can be reduced somewhat by rigidly mounting the probes. However, such mounting is not always possible, and even with extremely rigid fixturing, ambient temperature changes can cause movements of 0.010 inches or more. Such movements typically result in corresponding errors in the thickness measurements. Therefore, there is a need for an ultrasonic ranging system capable of compensating for relative movements between either a pair of spaced apart sensors, or a sensor and a reference position.